Bryant H N, Russell A P, Laroiya R, Powell G L
Provincial Museum of Alberta, Edmonton, Canada.
J Morphol. 1996 Sep;229(3):289-308. doi: 10.1002/(SICI)1097-4687(199609)229:3<289::AID-JMOR4>3.0.CO;2-U.
All carnivorans retract and protract their claws. In felids and some viverrids the claws of digits II through V of both the manus and pes have a larger arc of rotation than those of other carnivorans; the claws retract to the lateral side of the middle phalanx rather than onto its dorsal surface as in most other carnivorans. This condition should be termed hyper-retraction. Morphological features of the middle and distal (ungual) phalanges that have been purported to be necessary for hyper-retraction in felids vary considerably among digits within the manus and pes. These features include the lateral projection of the distal head and the asymmetry of the shaft of the middle phalanx, and the oblique orientation of the articular surface on the distal phalanx. None of these features is necessary in every instance for hyper-retraction, and some of the variation in these features is associated instead with protraction. Differences among digits in the orientation of the articular surface on the distal phalanx are associated with differences in the degree to which the claws must move laterally to rotate from the protracted to the retracted position. Differences in the orientation of the distal head on the middle phalanx are associated with the spreading of the claws during protraction. The manual claws are hook-shaped, whereas the pedal claws are more blade-like; this morphological difference is associated with differences in function between the manus and pes. In the manus the medial claws have a larger radius of curvature and a smaller angle of arc as compared to the more lateral claws; in the pes, the claws on digits III and IV have larger radii of curvature and smaller angles of arc. Digit I of the manus lacks the hyper-retraction mechanism; nonetheless, this digit shares many of the attributes that are associated with this mechanism.
所有食肉动物都会伸缩它们的爪子。在猫科动物和一些灵猫科动物中，手部和足部的第二至五指的爪子比其他食肉动物的爪子有更大的旋转弧度；爪子缩回时位于中节指骨的外侧，而不像大多数其他食肉动物那样缩回到其背表面。这种情况应称为超缩回。在猫科动物中，中节和远节（爪）指骨的形态特征被认为是超缩回所必需的，但在手部和足部的各指之间差异很大。这些特征包括远节指骨头的侧向突出、中节指骨骨干的不对称以及远节指骨关节面的倾斜方向。这些特征并非在每种情况下都是超缩回所必需的，而且这些特征的一些变化反而与伸展有关。远节指骨关节面方向的指间差异与爪子从伸展位置旋转到缩回位置时向侧面移动的程度差异有关。中节指骨上远节指骨头方向的差异与爪子伸展时的张开有关。手部的爪子呈钩状，而足部的爪子更像刀片状；这种形态差异与手部和足部的功能差异有关。在手部，内侧爪子与外侧爪子相比，具有更大的曲率半径和更小的弧度角；在足部，第三和第四趾上的爪子具有更大的曲率半径和更小的弧度角。手部的第一指缺乏超缩回机制；尽管如此，该指与这种机制相关的许多特征相同。
